Electronic phase shifter for vhf-uhf frequencies



R. H. GEIGER Oct. 31, 1961 ELECTRONIC PHASE SHIFTER FOR VHF-UHF FREQUENCIES Filed March 25, 1958 INVENTOR Raw/yea #667661? ATTORNEY V ass st! Patented Oct. 31, 1961 ice 3,007,077 ELECTRONIC PHASE SI-HFTER FOR VIE-UHF FREQUENCIES Richard H. Geiger, Emerson, N.J., assignor to Roger White Electron Devices, Inc., Haskell, N.J., a corporation of New Jersey Filed Mar. 25, 1958, Ser. No. 723,832 2 Claims. (Cl. 315-3.5)

This invention relates in general to the broad field of traveling wave tubes having helical wave structures and is more particularly directed to means within the tube for rapidly shifting the phase angle of an electromagnetic Wave traveling down the helix relative to its initial input phase angle.

In my co-pending application, Serial No. 649,855, filed April 1, 1957, now Patent No. 2,930,932, granted March 29, 1960, there was disclosed an apparatus for shifting in phase an electromagnetic Wave by inserting into the transmission line a slow Wave structure provided with an electron cloud of controllable density. The electron cloud effects a change in the dielectric constant of that space in the vicinity of the wave structure thereby altering the propagation velocity of the Wave in the vicinity of this electron cloud. However, in this mode of operation the helix lies Within the electron cloud so that it is subject to heating effects produced as a result of the electron bombardment thereof. Such heating effects reflect themselves in PR losses, with the temperature of the helix rising considerably above room temperature, thus reducing the efficiency of the operation of the phase shifting apparatus. A further consideration is the fact that the electron cloud dispersed about the helix interacts therewith in an axial, radial and circumferential manner, so that in effect there are three degrees of freedom of the electron cloud.

The present invention contemplates a phase shifting electron discharge device wherein an electron beam is generated which flows substantially in an axial direction with respect to the helically wound coil and is centrally located or surrounded thereby. By causing the velocity of the electron beam to travel at a relatively slow rate as compared to the signal on the helix, any electromagnetic Wave introduced into and propagated down the helix will undergo a substantial change in velocity or phase because of the relative interaction of the wave and beam with respect to each other. Since the beam is a concentrated one, flowing only in an axial direction relative to the helix, there will only be an interaction of the beam with the helix in the axial direction. Hence the beam has only one degree of freedom which requires controlling.

The electron density in apparatus of the typedescribed supra can be given when simple approximations are made:

Where J=current density at the cathode v=average drift velocity for the electrons e=e1ectronic charge It can be shown that the differential phase shift on a helical line is given by,

(hhu)L=A Where: A=differential phase shift in radians h0=phase constant with no electrons present emf hu=phase constant in present of the electrons cm.- L=length of the interaction space in cm.

In general, if a helical line is employed,

W 2 h=B0 cot (1-% where,

21 B =phase constant of free space= 'y=free space wavelength cot g0 (11') X (helix diameter in inches) (turns per in.) W =41rf f=Signal frequency W =plasma frequency for the electron gas Also, w-35 10(N) From these relationships it may be seen that by varying the electron density, N, we can change the phase of the signal on the helix. The anode voltage controls the electron density and thereby the phase shift.

It is therefore one object of the invention to provide improved apparatus in an electron discharge device having a helically Wound coil disposed therein for efiiciently controlling the phase angle of an electromagnetic wave when propagated along the helix.

Another object of the invention is to provide an electron discharge device apparatus, including a helically Wound coil, for producing an axial magnetically confined electron beam flow with low velocity for interaction With the surrounding helically wound coil and the wave propagated thereon.

A still further object of this invention is to provide an electron discharge device having a helically wound structure and a magnetically confined electron beam surrounded thereby which is rugged, small, efficient, easily fabricated and which permits the helix therein to operate at substantially room or ambient temperatures.

Other objects, advantages and modes of operation will become apparent from a study of the specifications and accompanying drawings wherein:

FIG. 1 shows schematically phase shifting means according to the invention;

FIG. 2 shows an elevation in section of an electron discharge device having phase shifting means therein according to the invention.

Referring now specifically to FIG. 1 there is shown a schematic of the phase shifting device according to the invention and generally designated by the reference numeral 10. An indirectly heated cathode 11 produces an electron beam 12 which is controllably confined by an axial magnetic field produced by circumferential magnetic core cylinder 13. The confined electron beam 12, after first emitted from cathode 11, is accelerated by a first accelerating electrode 14 at a substantially high velocity caused by a positive accelerating voltage V, applied thereto. The electron beam is subsequently decclerated by decelerating electrode 15 to a substantially low velocity caused by the relatively low positive voltage V applied thereto, as compared to the voltage V The decelerated electron beam 12 then enters the space about which the helix 16 is Wound. The helix i6 is relatively tightly wound, with a pitch preferably substantially less than its diameter. The helix coaxially surrounds the confined electron beam, and the wave propagated along the helix reacts therewith to undergo a substantial change in phase. The electron density of the beam (KN) is inversely proportioned to the electron drift velocity (v) and directly proportional to the beam current (J) so that a slow beam would be ideal for giving the maximum electron density. Ultimately the beam is collected by a collector 17 which has a relatively low positive potential V with respect to the cathode 11.

The electron beam velocity and density are controllable by the application of voltage variations at the acceleration and deceleration electrodes 14 and 15. The change in beam velocity and density effects a phase change of the propagated wave along the helix.

In FIG. 1 there is shown a generally commercial type tube 19 embodying the principles of this invention and constructed in accordance therewith. An evacuated glass bulb 24) has mounted therein an electron gun assembly 21 consisting of an indirectly heated oxide coated cathode 22 for emitting a beam of electrons, an accelerating electrode 23 and a decelerating electrode 24, each of which functions in accordance with the description aforementioned. There is further mounted within the glass bulb or housing a tightly wound ribbon type helix 25 having an input electrode 26 and an output electrode 27 appearing at the glass bulb interfaces and sealed therewith in accordance with techniques developed in the tube making art. A magnetic core coaxially surrounds the helix and produces an axial magnetic field which confines the beam axially within the helix.

An anode or collector electrode 30 appears at the extreme end of the glass bulb 20 and has generally a positive potential for the purpose of collecting the electrons emitted by the cathode. The anode electrode voltage as well as the acceleration and deceleration electrode voltages may be altered, as previously explained, to effect a change in the phase velocity of the wave propagated along the helically wound coil. With reasonable modulating voltages applied to these electrodes, it is possible to obtain at VHF-UHF frequencies large (180) phase shifts at practical beam currents. Another factor is that rapid (megacycle) rates of phase variation are possible since the device or apparatus is operative in a vacuum and only short lengths of helices are required.

While only a preferred embodiment of the present invention has been shown and described, other embodiments are contemplated and numerous changes and modifications can be made therein without departing from the spirit of the invention as set forth in the appended claims.

What is claimed is:

1. In apparatus for shifting in phase an electromagnetic wave, an electron discharge device comprising: a cathode electrode for generating an electron beam within the discharge device; a collector electrode for receiving the electron beam; a helically wound coil interposed between the cathode electrode and collector electrode for receiving and propagating along the surface thereof an electromagnetic wave; electron accelerating means positioned adjacent said cathode for accelerating the electron beam toward said slow wave structure; electron decelerating means interposed between said accelerating means and said helically wound coil; means for applying a relatively loW DC. voltage to said decelerating means to reduce the axial velocity of said electron beam to a speed which is relatively low compared to the axial speed of propagation of the electromagnetic wave along said helically wound coil; and magnetic field generating means for developing an axial magnetic field to confine the electron beam in proximity to the helically wound coil, said beam functioning to vary the dielectric constant adjacent the coil to thereby provide a shift in the phase of the electrcr magnetic wave propagated along said coil.

2. In apparatus for shifting in phase an electromgnetic Wave, an electron discharge device comprising: a cathode electrode for generating an electron beam within the discharge device; a collector electrode for receiving the electron beam; a slow wave structure interposed between the cathode and collector electrodes for receiving and propagating along the surface thereof an electromagnetic wave; electron accelerating means interposed between said slow wave structure and cathode for accelerating the electron beam generated by the cathode; electron decelerating means positioned between said accelerating means and said slow wave structure; means for applying a relatively low DC. voltage to said decelerating means to reduce the speed of the electron beam to a value substantially less than the slow wave speed of the electromagnetic wave along said slow wave structure; and magnetic field generating means for developing an axial magnetic field to confine the electron beam within close proximity of the slow wave structure said electron beam providing a variable dielectric adjacent said slow wave structure whereby the phase of the electro-magnetic wave propagated along the said structure may be varied.

References Cited in the file of this patent UNITED STATES PATENTS 2,578,569 McCarthy Dec. 11, 1951 2,595,698 Peter May 6, 1952 2,636,948 Pierce Apr. 28, 1953 2,753,481 Ettenberg July 3, 1956 2,762,948 Field Sept. 11, 1956 2,794,151 Kumpfer May 28, 1957 2,806,975 Johnson Sept. 17, 1957 2,811,664 Kazan Oct. 29, 1957 2,842,703 Preist July 8, 1958 

